Introducing new cat

Hi, i have a 2 year old cat., M neutered he spends time outside but is also indoor and just recently got a new cat (11 weeks)M not neutered he’s got his first round of shots, and the vet told me i’d be okay to start introducing around this time, i’ve been exchanging scents. but my 2 year old is out a lot so i kinda have to work on introducing them when he’s home, they’ve seen each other and the other day i lost the kitten and he ended finding himself upstairs under the bed along with 2 year old, when i found him they were both down there but nothing happened besides maybe some growling for 2 year old cat, immediately when i realized i quickly grabbed the kitten. i keep the kitten downstairs with his own area, food and litter box, completely separate from the whole house, i sometimes let him upstairs when the 2 yr old is outside, to get familiar and also hang out with our dogs, today i had them in the same room, and separated, the kitten was in his “mansion” and the 2 year we placed in the couch with good distance, they only could see each other, the kitten was just meowing a lot wanting to get out of his “mansion”. the 2 yr old just sat and watching, we offered him a treat for good behavior, and didn’t eat it, soon after he kinda started growling, he hissed at me as i was walking up to him with nothing in my hand, my bf is sitting next to him and pets him, then his kinda just starts loafing and closing his eyes, i don’t really know how to take in how the interaction went, he never actually hissed at the kitten, but did growl. eventually he left the room.

i know its early to tell wether or not it going well, and still got a ways to go, but what should i consider trying? and avoiding, i feel like because the 2 year spends alot of time outside we arent being very consistent, so it like one step forward, and two steps back ?!